Abstract

A layer of doped or undoped germanosilicate glass is formed on a substrate and the layer of germanosilicate glass is thermally treated in steam to remove germanium from the germanosilicate glass, and thereby raise the reflow temperature of the germanosilicate glass so treated. The layer of germanosilicate glass on the substrate may be a nonplanar layer of germanosilicate glass. When thermally treating the nonplanar layer of germanosilicate glass in steam, the layer of germanosilicate glass may be planarized simultaneously with the removal of germanium from the planarized germanosilicate glass. This process may be repeated to create a hierarchy of reflowed glass where each underlying layer reflows at a higher temperature than the next deposited glass layer. The steam thermal treatment step may be preceded by a thermal pretreatment of the layer of germanosilicate glass in at least one of a noble gas and nitrogen gas, to reflow the layer of germanosilicate glass. The thermal pretreating step may partially planarize the nonplanar layer of germanosilicate glass, and the thermal treating step may then fully planarize the partially planarized germanosilicate glass. Alternatively, the thermal pretreating step may fully planarize the layer of germanosilicate glass and the thermal treating step may then remove germanium from the fully planarized germanosilicate glass.